Surface rumples and band gap reductions of cubic BaZrO_3 (001) surface studied by means of first-principles calculations

Electronic properties of the （001） surface of cubic BaZrO3 with BaO and ZrO2 terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO2-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO2-terminated surface. Results of surface energy calculations reveal that the BaZrO3 surface is likely to be more stable than the PbZrO3 surface.

An ISGW Filtering Antenna with Spurious Modes and Surface Wave Suppression for Millimeter Wave Communications

In this paper,an integrated substrate gap waveguide(ISGW)filtering antenna is proposed at millimeter wave band,whose surface wave and spurious modes are simultaneously suppressed.A secondorder filtering response is obtained through a coupling feeding scheme using one uniform impedance resonator(UIR)and two stepped-impedance resonators(SIRs).To increase the stopband width of the antenna,the spurious modes are suppressed by selecting the appropriate sizes of the ISGW unit cell.Furthermore,the ISGW is implemented to improve the radiation performance of the antenna by alleviating the propagation of surface wave.And an equivalent circuit is investigated to reveal the working principle of ISGW.To demonstrate this methodology,an ISGW filtering antenna operating at a center frequency of 25 GHz is designed,fabricated,and measured.The results show that the antenna achieves a stopband width of 1.6f0(center frequency),an out-of-band suppression level of 21 dB,and a peak realized gain of 8.5 dBi.

Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca2CuO2Cl2

The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.

Surface defect gap solitons in two-dimensional optical lattices

We investigate the existence and stability of surface defect gap solitons at an interface between a defect in a two-dimensional optical lattice and a uniform saturable Kerr nonlinear medium. The surface defect embedded in the two-dimensional optical lattice gives rise to some unique properties. It is interestingly found that for the negative defect, stable surface defect gap solitons can exist both in the semi-infinite gap and in the first gap. The deeper the negative defect, the narrower the stable region in the semi-infinite gap will be. For a positive defect, the surface defect gap solitons exist only in the semi-infinite gap and the stable region localizes in a low power region.

Surface defect gap solitons in one-dimensional dual-frequency lattices

We study the surface defect gap solitons in an interface between a defect of one-dimensional dual-frequency lattices and the uniform media. Some unique properties are revealed that such lattices can broaden the region of semi-finite gap, and the semi-finite gap exists not only in the positive and zero defects but also in the negative defect; unlike in the regular lattices, the semi-finite gap exists in the positive and zero defects but does not exist in the negative defect. In particular, stable solitons exist almost in the whole semi-finite gap for the positive and zero defects. These properties are different from other lattices with defects. In addition, it is found that the existence of surface dual-frequency lattice solitons does not need a threshold power.

Distinct Superconducting Gap on Two Bilayer-Split Fermi Surface Sheets in Bi_2Sr_2CaCu_2O_(8+δ) Superconductor

High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is～2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.

LPE Growth of InAsPSb on InAs:Melt Composition,Lattice Mismatch and Surface Morphology

The LPE growth of quaternary InAs11-x-yPxSby with x = 0.2 and y = 0.09 on InAs substrate has been studied. This composition is very suitable for the laser and detector applications at about 2.5 μm. We show that in InAsPSb/InAs system there is a determinate relation between the surface morphology and the lattice mismatch of the epi-wafers, by which we can easily control the melt composition to grow high quality hetero-structures. The reason has been discussed. The p-n junctions with fairly good carrier profile have been prepared in this system.

Analytical calculation of electromagnetic, torque for surface mounted permanent magnet brushless motors

With the air gap magnetic field distribution of surface mounted permanent magnet （PM） motors obtained using an analytical technique, the instantaneous electromagnetic torque and its corresponding components are investigated with the Maxwell stress tensor method. Accurate results can easily be achieved using the proposed method without using the tedious finite element analysis （FEA）. In this paper, the electromagnetic torque of a surface mounted PM motor with two phases energized is decomposed into four torque components. This technique is useful not only for the design and optimization of the permanent magnet motor, but also for the choice of control strategy.

3D v_P and v_S models of southeastern margin of the Tibetan plateau from joint inversion of body-wave arrival times and surface-wave dispersion data

A new 3D velocity model of the crust and upper mantle in the southeastern （SE） margin of the Tibetan plateau was obtained by joint inversion of body- and sur- face-wave data. For the body-wave data, we used 7190 events recorded by 102 stations in the SE margin of the Tibetan plateau. The surface-wave data consist of Rayleigh wave phase velocity dispersion curves obtained from ambient noise cross-correlation analysis recorded by a dense array in the SE margin of the Tibetan plateau. The joint inversion clearly improves the Vs model because it is constrained by both data types. The results show that at around 10 km depth there are two low-velocity anomalies embedded within three high-velocity bodies along the Longmenshan fault system. These high-velocity bodies correspond well with the Precambrian massifs, and the two located to the northeast of 2013 Ms 7.0 Lushan earthquake are associated with high fault slip areas during the 2008 Wenchuan earthquake. The aftershock gap between 2013 Lushan earthquake and 2008 Wenchuan earthquake is associated with low-velocity anomalies, which also acts as a barrier zone for ruptures of two earthquakes. Generally large earthquakes （M 〉 5） in the region occurring from 2008 to 2015 are located around the high-velocity zones, indicating that they may act as asperities for these large earthquakes. Joint inversion results also clearly show that there exist low-velocity or weak zones in the mid-lower crust, which are not evenly distributed beneath the SE margin of Tibetan plateau.

The Surface Reactivity and Electronic Properties of Small Hydrogenation Fullerene Cages

Density functional theory calculations within the G03W package, with B3LYP exchange functional and applying basis set 6 - 31 G (d,p) are performed. The surface reactivity and electronic properties of endo-hydrogenation and exo-hydrogenation fullerene cages are studied. It is found that the surface reactivity of mono-hydrogenation fullerene cages is larger than the surface reactivity of un-hydrogenation fullerene cages and the later is larger than the fully hydrogenation fullerene cages. In addition, the calculations show that the endo-hydrogenation fullerene cages possess the same band gaps as the un-hydrogenation fullerene cages, however, the exo-hydrogenation is reduced the band gaps of the un-hydrogenated fullerene cages form ~7 eV to ~5 eV.

Surface effect on band structure of magneto-elastic phononic crystal nanoplates subject to magnetic and stress loadings

This paper presents a theoretical model for the size-dependent band structure of magneto-elastic phononic crystal(PC)nanoplates according to the Kirchhoff plate theory and Gurtin-Murdoch theory,in which the surface effect and magneto-elastic coupling are considered.By introducing the nonlinear coupling constitutive relation of magnetostrictive materials,Terfenol-D/epoxy PC nanoplates are carried out as an example to investigate the dependence of the band structure on the surface effect,magnetic field,pre-stress,and geometric parameters.The results show that the surface effect has promotive influence on dispersion curves of the band structure,and the band gaps can be improved gradually with the increase in the material intrinsic length.Meanwhile,the band gaps exhibit obvious nonlinear coupling characteristics owing to the competition between the magnetic field and the pre-stress.By considering the surface effect and magneto-elastic coupling,the open and closed points of band gaps are found when the lattice constant to thickness ratio increases.The study may provide a method for flexible tunability of elastic wave propagation in magneto-elastic PC nanoplates and functional design of highperformance nanoplate-based devices.

Electronic Structure of Gallium Phosphide Nanocrystals Core and (001)-(1 ×1) Oxidized Surface

The electronic structure of III-V zinc blend Gallium Phosphide nanocrystals is investigated using ab-initio density functional theory coupled with large unit cell for the core and surface parts. Two kinds of cells are investigated: multiple Bravais and multiple primitive cells. The results show that both energy gap and valence band width depend on the shape of the nanocrystal. Results also revealed that most electronic properties converge to some limit as the size of the large unit cell increases. Furthermore, the results have shown that the cohesive energy is decreasing with increasing size of nanocrystals. The core part is more degenerate, with larger energy gap and smaller valance and conduction bands than the surface.

Near Infrared Fluorescence Enhancement by Local Surface Plasmon Resonance from Arrayed Gold Nanoblocks

The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass substrates, to clarify the gap mode effect on the fluorescence enhancement. In the substrate with Dimer type Au nanoblock arrangement, average total fluorescence intensity was larger by 10.0, 2.4, and 12.4 times for non-polarized, P- and S- polarization as compared with that on a glass substrate alone, respectively. These findings suggested that enhancement of excitation light intensity at nanogap in the Dimer type Au nanoblock arrangement affected the fluorescence intensity. Average total fluorescence intensity, on the other hand, was smaller by 0.63 times as compared with that on a glass substrate alone in the checkerboard type Au array. It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement. We have firstly achieved the NIR fluorescence enhancement by LSPR due to the gap mode.

Ag与p型GaP欧姆接触的表面特性分析

在p型GaP表面制作Ag电极,并利用退火环境令金属和半导体的接触界面产生良好的欧姆接触。通过扫描电子显微镜(SEM)、俄歇电子能谱(AES)以及X射线光电子能谱(XPS)的表征分析与对比,研究了不同退火环境对欧姆接触表面特性的影响。结果表明:退火时间过短,获得能量自由移动的原子移动面积小,不利于提高样品表面致密性;退火温度过高,欧姆接触表面的晶粒又容易发生球聚现象,造成样品表面的粗糙程度加剧。另外,在退火过程中,发生的相互扩散、形成化合物和合金相以及氧化反应也会对欧姆接触表面特性产生影响。其中,氧化反应较其他反应更为剧烈,对比接触电阻率的影响更大。因此,适宜的退火环境和有效控制氧化反应是增强欧姆接触性能的关键。

表贴式高速永磁同步电机失磁故障及磁体选区渗重稀土研究

针对表贴式高速永磁同步电机永磁体在受到高温、强退磁磁场等因素影响易产生局部不可逆失磁故障问题,本文基于有限元分析方法,分别建立了一台24 kW表贴式高速永磁同步电机的二维和三维仿真计算模型,在计及该电机在各类不同的退磁因素作用下,确定了电机磁体发生局部不可逆失磁故障的位置,并预测了磁体的进一步失磁扩散趋势。对比了电机在有无失磁故障情况下的空载气隙磁密和反电动势,并研究磁体不可逆失磁故障对电机运行的影响。由于永磁体易在部分区域发生不可逆失磁,故本文将磁体材料更换为较低牌号,并运用选区渗重稀土技术改善易失磁区域材料特性来提升磁体整体抗失磁能力。在此基础上,探究了更为合理的重稀土渗入区域及渗入梯度,从而保证在不失电机性能的前提下,实现了重稀土元素的极限应用,为表贴式永磁电机磁体选区渗重稀土技术提供了参考。

星型GAP与固体推进剂填料的表界面性能

采用动态接触角和界面张力仪,研究了星型GAP(S-GAP)与AP、RDX和HMX之间的表界面性能。结果表明,星型GAP与固体填料间的界面张力关系为γSL(S-GAP/RDX)<γSL(S-GAP/HMX)<γSL(S-GAP/AP);星型GAP与固体填料间的粘附功关系为Wa(S-GAP/AP)<Wa(S-GAP/RDX)<Wa(S-GAP/HMX)。星型GAP与固体填料间的粘接界面的作用力主要为界面分子间作用力。S-GAP与RDX、HMX之间主要由于氢键、偶极等作用而形成较强的界面作用;S-GAP与AP间由于分子间作用力较小,故界面作用较弱。

基于面结构光的飞机舱门间隙测量技术与应用

针对复杂试验环境下,战机舱门间隙非均匀变形动态测量难度大、精度要求高的问题,提出了基于面结构光的飞机舱门间隙测量方法,研究了条纹投影结构形面测量方法,包括在不需要空间相位展开过程或任何先验信息的情况下搜索包裹相位图中每个有效像素的立体对应和绝对条纹顺序,生成初始视差图和绝对相位图并进行了视差优化;建立了立体结构光模型,利用视差图和绝对相位图计算三维坐标。对得到的数据进行处理,包括建立被测件的物理坐标系,曲面截取以及对间隙位移量提取。设计了两种标准间隙,对本文方法的合理性和有效性进行了验证,可以对任意曲面和动态场景进行快速、准确的间隙和阶差的测量。将本方法应用于某飞机舱门间隙变形的测量中,获得了实际的变形位移量。

表面接枝GAP改性超细铝粉的制备与性能(英文)

用二异氰酸酯作桥,通过—OH和—NCO基团间的连串缩合反应,经过接枝含能端羟基叠氮缩水甘油醚（GAP）,改性了超细（1-2μm）铝粉表面。研究了接枝GAP铝粉的表面性质,与含氟粘结剂的相容性及70℃水中稳定性。结果表明,接枝前后的铝粉表面静态水滴接触角分别为0-25.7°和109.9°,表面接枝后,铝粉表面性质从亲水改变为疏水。接枝GAP的铝粉与含氟粘结剂有更好的相容性。在70℃水中15 min后,未经处理的铝粉有39.8%的活性铝被氧化,而经过GAP接枝改性的铝粉在70℃水中60 min后只有1.4%的活性铝被氧化,显示接枝GAP的铝粉可有效保护铝粉在苛刻的热水条件下不被氧化。

Au/Au-Be与GaP欧姆接触的表面分析

用表面方法(SEM,SAM,XPS)研究了在不同温度热处理后Au/Au Be与GaP接触的特性.结果显示,Au Be与GaP接触的界面特性强烈地依赖于热处理温度.经550℃热处理过的界面均匀、平整,其I V特性斜率大,接触电阻小;经较高温度(580℃)热处理过的表面有结晶团状物产生,晶粒变粗,接触电阻增大.AES和XPS分析表明,经540～550℃温度热处理后,界面生成Au Ga P化合物;Be原子由表面向界面扩散,在界面处出现最大值.

局域共振超材料表面波屏障带隙特性与隔振性能

为有效解决轨道交通运营引发的地面振动问题,基于声学超材料概念提出一种局域共振超材料表面波屏障(locally resonant metamaterial surface wave barrier,简称LRMB)隔振方法,并采用混凝土和橡胶垫层构造出屏障结构。根据半无限空间弹性动力学理论,推导LRMB带隙计算的解析式,分析橡胶垫、混凝土参数对LRMB带隙特性的影响规律。基于轨道交通地面振动实测数据,探讨LRMB的隔振效果。研究结果表明:LRMB表面波带隙产生主要与其竖向振动有关,基于该模式建立的带隙计算方法是准确的;LRMB橡胶垫厚度增大,带隙起始频率降低,带隙宽度增大;LRMB橡胶垫宽度增大,带隙起始频率升高,带隙宽度减小;LRMB混凝土质量增大,带隙起始频率降低,带隙宽度增大;LRMB原胞数量增多,隔振效率提升,隔振效率达到20~25 dB;以济南轨道交通1号线工程为例,采用LRMB后地面振动衰减可达70%~80%,验证了LRMB的良好隔振性能。